The present invention relates to plastic containers and in particular to a plastic container having a reinforcing ring in its base to strengthen the base.
In recent years, the use of plastic containers for beverages, and particularly carbonated beverages, has increased dramatically. These containers are typically blow molded from an injection molded polyethylene terephthalate (PET) preform. A difficulty, however, with the use of plastic containers for carbonated beverages is in providing sufficient strength in the container base. The internal pressure in a container filled with a carbonated beverage can range from approximately 60 psig at room temperature to as high as 100 psig at 100.degree. F. These pressures can produce deformation of the base portion of the container which may result in a container which does not have a flat bottom surface perpendicular to the upright axis of the bottle such that the bottle will no longer stand upright on a horizontal supporting surface. In addition to stability problems with a deformed base, when the container base is deformed, the volume of the bottle typically increases. This results in a lowering of the liquid fill line such that consumers may be led to believe that the bottle was not properly filled or sealed.
One solution of the problem of distortion in the container base is to blow mold the container with a hemispherical base extending downward from the side wall of the container. In order to support a container with a rounded hemispherical bottom, it is necessary to attach a second plastic piece to the rounded bottom to function as a support stand for the bottle. This second piece, often referred to as a base cup, includes a bottom wall and a generally cylindrical upstanding wall extending upwardly from the bottom wall. The base cup is telescoped over the hemispherical end of the container and typically conceals the rounded hemispherical end. The hemispherical end of the container is often glued to the bottom wall of the base cup to hold the base cup to the bottle. This bottom wall serves as a planar surface upon which the container can be supported in an upright manner.
A major disadvantage with a base cup container is the additional material cost required to form the base cup. Base cups are typically molded of polyethylene which has recently increased dramatically in price. The polyethylene base cup contributes almost half of the container material costs while representing approximately one third of the material weight. Another difficulty with the use of PET bottles and polyethylene base cups is recycling the plastic materials in the container. Before the plastic can be reground, the PET bottle must be separated from the polyethylene base cup.
The problems associated with base cup containers have encouraged efforts to develop one piece self supporting containers. One such container is disclosed in U.S. Pat. No. 3,598,270 issued to Adomaitis. The Adomaitis container has a generally hemispherical bottom with a plurality of hollow legs extending downwardly from the hemispherical base forming feet at the lowermost surface of the container. This container also has disadvantages. It is difficult to obtain adequate flow of plastic into the foot cavities in the mold to fully form the container feet without over compensating and wasting plastic material in the base of the container. The possibility of stress cracking in the container base is a definite problem and the pressure of the container contents tends to distort the base so that it will not sit flat.
Accordingly, it is an object of the invention to provide a container which can be more economically produced than a typical base cup container or a typical one-piece container.
It is a further object of the invention to provide a container in which stress cracking of the base is eliminated and the plastic is efficiently distributed in the container.
Another object of the invention is to provide a non-base cup container in which distortion of the base is avoided by a reinforcing ring held in place in the base by the pressure of the container contents.
It is a feature of the present invention to provide a blow molded bottle with a plastic reinforcing ring attached to the base to strengthen the base.
It is an advantage of the invention that the entire container can be constructed of one plastic material such that separation of the container and the reinforcing ring is not necessary prior to recycling the material used in the container.